1. Field of the Invention
The present invention relates generally to fluid hydraulic devices and methods of sealing high pressure fluids. Specifically, the present invention provides a fluid apparatus for transforming the magnitude of an input or applied pressure to at least one output or supply pressure, which pressure is a predetermined multiple or fraction of the input pressure. Using the design of the present invention, each of the individual seal elements in the transformer experiences a pressure differential which is a predetermined constant fraction of the total input pressure, thereby allowing the total number of seals to remain effective against very high pressures over a long period of time.
2. DESCRIPTION OF THE PRIOR ART
In the field of fluid hydraulics, the need for pressure intensifiers and reducers is well known. One type of pressure intensifier utilizes mechanical elements which act on the hydraulic fluid to increase its energy content and pressure. This type of pressure reducer is based on a pressure regulator which utilizes external mechanical control elements to absorb or control the flow rate of the hydraulic fluid in order to reduce its energy content and pressure.
Another well known type of pressure intensifier or reducer involves an assembly of pistions in which each piston includes at least two opposing surfaces of different surface areas. By applying pressure to the smaller surface, the resulting force on the pistion creates a reduced force at the larger surface. Conversely, by applying pressure to the larger surface, an increased pressure results at the smaller surface. Piston-type intensifiers and reducers have the advantage of preserving the energy content of the fluid while inherently performing pressure amplification or reduction. Piston-type intensifiers and reducers are preferred over the other types of devices involving external control elements because of the reliability and predictablility associated with their operation.
To obtain multiple increments of pressure reduction or intensification requires the use of multiple separate pistons serially connected together. Each piston in the series operates independently of the others, and each receives its input pressure from the preceding piston and supplies its output pressure to the following piston. Each piston in the series therefore creates its own independent influences on the total performance of the system. Because of the serial connection and the independent influences of each, some difficulty exists in obtaining certain desired and controllable effects such as predetermined pressure increments across the seal elements used in the series.
In the field of fluid seal assemblies, which are used for sealing static or dynamically moving parts against the application of pressure differentials, there are no known reliable and economic seal elements which remain effective against the application of extremely high pressure differentials. Seal failure is directly related to the magnitude of the pressure differential which the seal must withstand. High pressure seals typically fail after relatively short periods of use because they are charcteristically unable to withstand extremely high pressure differentials, particularly when relative movement between the seal element and one of the parts to be sealed is involved. Even when a plurality of seals are ganged or connected together, the majority of the pressure is typically withstood by only one seal of the group.
One solution to the above-discussed problems is shown in U.S. Pat. No. 4,505,115, owned by the applicant of this invention and which, by this reference, is incorporated for all purposes. The hydraulic system shown in this Patent is capable of supplying a plurality of increments of intensified or reduced pressures on a static or a dynamic operating basis wherein each incremental pressure is operatively related to the other incremental pressures and to the input reference pressures by previously unattainable relationships. In particular, the aforementioned invention provides an integrated pressure transformer and seal assembly wherein each of a plurality of seals is required to withstand a predetermined constant fraction of the applied pressure whereby the total number seals remain effective against very high pressures and over a relatively long period of use.
Despite the advantages and advancements provided by the above-referenced invention, a number of problems remained in actual operation of the system. One problem was unavoidable leakage across the seal boundaries which seal the pistons within the cylinders. This leakage occured both when the transformer was activated by an input pressure, and when the input pressure fluctuated, or changed in magnitude. This leakage caused movement of the pistons such that they drifted within the cylinders. As the fluctuation of pressure continued, the pistons began to drift to either end of the cylinder in which the pistons are housed. If the pistons drift to one end of each of the cylinders, the pistons are no longer in pressure equilibrium. Therefore there is no predetermined pressure created in the chambers, and the fluid transformer ceases to operate as a pressure-reducing system. Prior to the invention shown in the present application, there was no known method of correcting this problem.
Another problem with the operation of the prior fluid transformer sealing system was the introduction of contaminants; small particles, gases and corrosive fluid entering the inner workings of the fluid transformer, referred to as fluid contamination. The introduction of fluid contamination to the fluid transformer system is initiated by leakage of high pressure fluid into the lower pressure chambers of the fluid transformer during operation. The introduction of contaminated fluid into the fluid transformer system interferes with its creation of predetermined pressures. It does this in several ways: (1) Particles can become lodged between the surface of the piston and the surface of the cylinder, preventing movement of the piston to pressure equilibrium. The contaminated particles, if sufficiently hard, can scratch the piston and cylinder surfaces during piston movement. The surface scratches, particularly on the cylinder, can cause further fluid leakage, and consequent piston drift. Contaminated particles can also lodge between the seal and the cylinder, causing small scratches and abrasions in the seal material. Under high pressure conditions, these scratches and abrasions are easily made larger, resulting in immediate failure of the seal. Scratches in the walls of the cylinders as a result of contaminated particles introduced into the system, can also cause scratches and abrasions in the seal material. In either case, damage to seals causes sudden seal failure and will render the fluid transformer inoperable; (2) Gas contaminants are introduced into the fluid transformer system by leakage across the seal elements, and by the introduction of soluble gas in the hydraulic operating fluid. When the fluid in the transformer is reduced in pressure, and as the input fluid pressure drops, the gas becomes insoluble, creating bubbles in the chambers. The gas is compressible under high pressure, and therefore causes significant piston movement or drift to the extremities of the piston housing, rendering the system inoperable; (3) Fluid contaminants can also be introduced into the fluid transformer system by leakage across seal elements, similar to the introduction of gas contaminants. The fluid contamination can be corrosive, and depending on the nature of the contaminants, the seals can be dissolved over time; metals used in the contruction can become eroded oxidized or otherwise destroyed. Prior to the present invention, there was no known method of purging or otherwise removing contaminated solids, gases or fluids from the fluid transformer.
Another problem with the operation of the prior fluid transformer sealing system was the additional shearing force, or extrusive force on the seal elements sealing the large diameter pistons and cylinders, due to the location of the seal elements on the pistons. During operation the seals located on the large diameter pistons experience two types of destructive forces. One force is frictional, the other is a result of pressure acting on the seal. The frictional force occurs opposite to the direction of the pistons' movement as the pistons move toward the large-diameter end in attaining an equilibrium condition. The pressure force on the seal comes from the pressure developed on the large-diameter piston end, and is also in the opposite direction of the pistons' movement. Since both forces act on a large diameter piston seal in the same direction, both forces act together in extruding or shearing the seal. Prior to the present invention, there was no known configuration of the fluid transformer that could reduce the combination of these forces, such that they would not operate additively to destroy the large-diameter piston seal.